1. Field of the Invention
The present invention generally relates to an image capturing device, in particular, to an image capturing device and a shading compensation method thereof.
2. Description of Related Art
With development in technology, digital cameras and smart phone have become mediums for modern people to record life stories and great moments. To provide more user-friendly features has been a core subject for each manufacturer of the aforesaid image capturing devices.
An optical sensing element such as a charge-coupled device (CCD) element or a complementary metal-oxide semiconductor (CMOS) element may be used in a conventional image capturing device for capturing light entering thereto through a lens. When the light passes through the lens, it may be refracted to produce an image on the sensing element. However, light refraction may cause energy loss so that the refraction angle passing through an edge of the lens is greater than that passing through a center of the lens. The produced image may then be clear in a center and fade off at edges. Such phenomenon is referred to as “vignetting” or “shading” in photography and optics, and may create such non-cohesive image and an adverse visual effect for the user.
Most of the conventional shading compensation algorithms are only adapted to single lens cameras, where one or more lookup tables interpolation mechanism is proposed, and parameters adopted for constructing the lookup table may be a fixed or a plurality of commonly-used light sources. Such lookup table mechanism may provide a solution associated with different color temperatures such as fade edges or color shifts on the produced image, and yet the interpolation parameters or the lookup table may need to be adjusted adaptively according to different light sources. Moreover, the frequency spectrum of different light sources may be drastically different. To adjust the interpolation parameters so that the lookup table satisfies all possible light sources may not be an intuitive implementation. If a scene image is captured under an unknown or composite light source, the shading problem remains unsolved.